Wheat ticked higher as fears of flooding in the US Plains after heavy rains supported the market although strong exports from Russia, the world's biggest supplier, limited gains.
The most-active soybean contract on the Chicago Board of Trade dipped 0.1 percent to $8.62 a bushel by 0335 GMT, having closed down 0.8 percent on Tuesday.
Wheat was up 0.3 percent at $5.16-3/4 a bushel, having closed up 0.2 percent on Tuesday and corn gave up 0.1 percent to $3.64-1/4 a bushel after finishing down 0.5 percent in the previous session.
The US Department of Agriculture will issue its supply and demand report for October on Thursday.
Analysts polled ahead of Thursday's report, on average, expect the USDA to increase its US corn and soybean yield and production forecasts as well as raise its US and world grain and soybean stocks projections.
The agency said 32 percent of the soybean has been harvested, behind market expectations.
Corn harvest has reached 34 percent, the USDA said, matching market expectations.
Soybeans came under additional pressure after US President Donald Trump on Tuesday reiterated threats to impose tariffs on $267 billion worth of additional Chinese imports if Beijing retaliates for recent US tariff actions.
Commodity funds were net sellers of CBOT corn, soybean, soymeal and soyoil futures contracts on Tuesday and were net even in wheat, traders said.
But the decline in soybean prices could result in buying.
"Chicago November soybean prices, like corn futures, sit on the precipice of triggering hefty buying," said Tobin Gorey, director of agricultural strategy, Commonwealth Bank of Australia.
Recent rains swamped some newly seeded winter wheat fields in parts of the Plains Wheat Belt, raising fears of some crop damage.
Russia's agriculture ministry has proposed speeding up an increase in the country's grain export capacity, part of efforts by one of the world's largest wheat exporters to move into new markets.
Russia aims to increase its grain export capacity by 25 million tonnes to 77.7 million tonnes by 2024, agriculture minister Dmitry Patrushev said at a meeting with President Vladimir Putin and other officials on Tuesday.
Russia has been boosting sales in recent years to markets in Asia, the Middle East and Africa, winning key tenders.